Properties: Bright blue, hygroscopic crystals. Above 38° changes to isomeric green modification. Loses 1H2O, forming trihydrate, at 51°. Absorbs O2 even when dry, forming a greenish-black oxychloride. Sol in water. Almost insol in concd HCl. On standing in soln it is oxidized by the water with liberation of H2. Keep well closed.

Use: In chromizing; in prepn of Cr metal; in catalysts for organic reactions; as O2 absorbent; in analysis.